The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems such as plasma-enhanced atomic layer deposition (PEALD) and plasma-enhanced chemical vapor deposition (PECVD) may be used to deposit and etch films on substrates such as semiconductor wafers. Some PEALD and PECVD systems include chandelier-type showerheads that supply precursor to a processing chamber.
The showerheads typically include a stem portion that extends into the processing chamber and a head portion connected to the stem portion. A cavity is formed behind the head portion between the head portion and an upper surface of the processing chamber. In other words, the showerhead creates dead volume in the cavity.
For continuum processes like PECVD, the cavity is not functionally a problem. However, for transient processes such as conformal film deposition (CFD) or ALD, the cavity stores chemistry that is emptied or exchanged in subsequent steps. Storage of the chemistry across the successive steps may result in time-varying contamination of the ambient. Reducing the cavity tends to bring the showerhead (which is usually powered with RF) closer to a top surface of the chamber (which is usually at ground). This can increase RF coupling to the chamber top surface. In some cases, the increased RF coupling can adversely impact the ability to strike plasma. Also the presence of stagnant chemistry in the cavity area can lead to deposition of films that eventually cause defects.